Method of and apparatus for neutralizing distortions of optical projections.



Yimnrnon or militaires ron nnurmmzme ms'rom'rons or omiten m I Jnc'rrojns.; '-v

1,2%?,623v t Y l l I-pecicaton ot-ill'ettcrs Patenti Illy 16,' 1918..

Application and :alle 21, 191s. smal mi. sanas.

To all 'whom it may concern. w stone and other distortion may be `counter;l

Be ila-known that I, DANIEL F. Cons'mcx, acted without substantiel-lj' imparing the 65- a citizen of the United States. and residentdeinition. In the ordinary practice the' of Brookline, in the county. of' Norfolk and transparency to be'px-ojected upon the screen State oflllfnssaclnisetts, have invented new S placed'pelpendllllal the'ptlal 11x13 and useful II-nproveinents in Methods of of the projecting lens,` and a little farther and Apparatus for Neutralizing- Distortions uw xy from the lens than its principal focus, of Optical Projections, of which'the followend the light from an electric are or other ing is a specification. llluminant is 'passed through the transpar- This invention relates to the method of, ency and the ,lens. Under these circumand apparatus for col-npensnting certain dis-` stances, .assuming for a n ioxnent aperfect tortions encountered in optical projection, lens, an ideal or mathematical*image is pro 65 and more particularly .to the method of and duced in space in a plane perpendicular tov apparatus for compensating the distortion the optical axis of the lens and a considof the projected image from an optical lanernble distance in front. ofthe lens. If a tern d'ue to thc fact that the central or screen is placed so as to coincide with this average ray from the optical lantern is not-1 image plane, a perfect, enlarged image geen 70- normal to the screen. metrically similar-'to the, transparency .itself In the nrt of optically projecting upon a will be 'for-med on the screen.

screen a magnified image of the photograph Strictly speaking, there is no other .point--`-*"r"" or other transparenc it. has become the cnsin space where .a true image is formed, and tom to place the optical lantern nbove the if'the screen is placed at any other position 75 level of the ypoint, upon the screen`which along theoption]anisngmnifzthe angle if;` coincides with the middle of the picture, in niakes witl'tlfe optical axis is changed 'h order that. the lantern may occupy less valnthe slightest amount, that is, if the screen 1s able space in the theater. or hall than vthe tipped, there lwill appear no tru-e image 'on point-immediately opposite the screen which the screen, that is; such pseudo image, as

is usually required for seating purposes. thereis, will he indistinct, and will lac-k It is also customary to place the screen what istechmcally called defin1cion. an .upright position substantially perpen- Practically, however, the ease is somewhat dicular to the normal line of vision to the different, since no lenses are perfect and average spectator. The resultingobli nity since the leyes of the spectators are 'at con.- 85 oincidcnee of the projection beam produces siderable distances ,from the screen, and it a distortion effect on the screen` known ,as the 'is therefore impossible to. detect minute keystone effect., so-called because a reclosses of defini-tion in the'image beyond a tangular figure at the object or transparency certain limiting point. The screen can, asv a is distorted in the projected image to a matter of fact, be movedthrongh considerfigure resembling an inverted keystone. able distances without appreeiably changing This keystone effect is due to the fact that,v the distinctness of the pictnreon .the- Screen, iall parts of the screen where it .intersects the and it can also be tipped to considerable rays are not equidistant Afrom the projection angles withoutl changingfappreciably the' lens, in other words, that the central ray is dstinctness of the picture.l y not normal to `the screen; and since the ralj's There exists, therefore,- a considerable re of the bea-rn leaving the projector diverge giron of space iin which it is-possible to getfrom the projector, the image 0nthose parts a practically distinct picture on the screen,v of the screen more remote from the projecand since throughout this region -theappean tor will be magnified to a greater extent' ance ofthe screen as regards distinctness of 100 than those parts nearer `the projector. More picture is not changed, it is appropriate for over, the sharpnesso definition also suffers practical purposes to speak always of the from-this Obliquity as will be pointed out image as if it were 'on 'the screen no matter later. Y' ,i what the position ofthe screen jchronf'ghout.A v It is the obj-ect of this invention` to ros the above mentionedfregon.ospeee-ni-ey be.: vide a method anlnennsfliy which the ey-i This'negion 'of surrounding theplonev of best definition inf-whichit is possible to .g'etvsut-iicie'ntl rdistnct pictures'on the screen regardless o the position of the screen in the region, or of its tip through moderate angles, will be called throughout this exposharp picture on the screen will simply be called 'the image. i

Although the image on the screen does not change appreciablyin distinctness throughout the whole region even with mod erate screen Obliquity, the size and shape of the image on the screen does not remain the same as the screen is moved in the before mentioned ways. If the screen is per audioular to the optical ums and is more inthe image region from a certain point to a point f will be distorted. The most noticeablechar'- acteristic of the distortion when the screen is oblique is the keystone ellect mentioned at the beginning,

Just as there is an image region, as above described, surround-ing the :mathematical image in space, so thereis a corresponding region surrounding the plano transparency in which i-t-can` be moved parallel to itself ness of the imageon the screen. Since, in distinction to the image, the plane transF parency following the technical terms of optics would be called the object, I will call t is region of space by analogy the object space.

The magnitude 'of the object space is in. general very much less than the Vmagnitude of .the image space, and since both oftheir limits are determined by the position at which the blurring of the image is noticeable it is clear that both spaces have very imperfectly defined boundaries.-

he magnitude of the yirnage'space corresponds to what is known in optical technology as depth of focusf. My methodof v overcoming the distortion known as the key-` stone e'ect can now be' ut in general terms.

The beam of light 1n the object s ace bears stamped upon it the ometrical slieracteristics of the'object. `tics become invisible 'durino thepass-age of the -light through the lens but they appear agam in the image space and produce on any screen inthe image space perpendcular to the opticalaxis, a m nied, Geometri? cally similar. image'of thenr-ject, ur problem, therefore, is to modify or `reconstruct the lens system insucha way that the image,

defined by a screen perpendicular to the-8x18,

- hese characteris-- along the optical axis, or slightly tipped, 1 Without appreciably changing the distinctisno longer 'geometrical-ly similar tothe ob ject but is distorted :in such a,V way that it contains within it what' mi ht be cal-led an.

inverse keystoneelfect,-t at is, `the distortion of the image beam is such that the produced on ascreen. j rpendxcular as i.

to t e axisfjin the image region would be distorted in such a way as to show a key stone efect of an opposite kind to that which the unmodified 'lens system would produce on the obliquescreen at the same point. i

The distortion `which we des-ire to produce in the image beam by the image pro uced on a screen laced in the image-region perpendicular tot 1e optical axis, is of a peculiar and unique type. It may bebriefly symbolized by saying that one set of equidist'ant parallel lines 1n the object remain equidistantimd parallel in the 1mage,'while the set of equcl'istant parallel'l said beam being tested lines perpendicular to thefrst'set in the object appear in the image `on the screen not 'as parallel but as converging toward a distant .poi-nt in the plane of the screen.

This type `of geometrical distortion is substantially that which occurs on the exhibiting screens in vconnnon practice when the screen is not perpendicular to the light beam, and hence as before mentioned one distortion may -be used .to neutralize the other. Y

It should be noticed'l 'that these two distortions which thus neutralize each other aredue to quite different causes, the one on the oblique screen being due to -the fact that all parts of the screen are not equidistant 'f from the projection lens, wh-ereas'the distortion of theimage beam is the direct result of a unique type of refraction. 4 'The simplest Way-to accoi-nplish the distortion of theimage beam before mentioned is by the substitution of torted virtual image for the object. 'For this purpose I have, among other methods, obtained goed results by the use of an optihereinater indicated,

AIn 'the accompanyiny drawin illustrate one embodiment of the invention i in diagrammatic form;-

Figure- 1 is a side elevation .in diagram,

partlyvbroken array, showing the relation of vsuch distortion;

Fig. 3 is a side elevation'similar to Fig. 1,

Fig. 4 is. a duce view similar to Ih'g.j 24,-

a properly dis- 116 cal element in thel 'shape ofa 'tipped Iin relation to the nsparency as which 12s, showing in diagram a method of correcting v such distortion showing the form of the corrected' projected and c represents the screen image. It will be noted that the central .line d of the light beam from the objective to thescreen is not norinal to the screen, consequently the projected iniage c upon the screen. will be in the shape of an inverted keystone as illustrated in F ig. 2, the lower partof the projected image c being more remote from the optical lantern than the upper part, and therefore magnified to a. greater extent. Since the' transparency or object b is normal to the central light beam d, the plane of Vthe real image would also be normal to the central light beam d as shown at c. T here will be a consequent loss o 4definition of theiniage c on the screen owing to the .fact that the screen image c is not in the same plane as the plane of the real iniagec.

In order to produce a distortion of the virtual image to counteract the distortion of the projected image on the screen, a ifefracting element, or elements, is introduced Alistview the transparency and the screen,

preferably near the transparency, capable of niagnifying or reducing the vii-tual image 1n substantially one 4.direction only, namely,

in the direction of distortion of the screen image, which magnification orreduction, or both, are qualitatively7 andy quantitatively suitable for neutralizing the distortion of the screen image.

The example of such refracting element illustrated in the drawings is a planoconrex cylindricalens L, the axis ofn'hicli is tipped relatively to the transparency-,thus producing a distortion ofthe virtual image similar to but opposite to that of 'the sci-een image. Such virtual imageis indicated diu- 'gramniatically atV b. The parts of the cylindrical lens L nearest the object b result iii a certain magnification of the virtual image, depending on the distance of the lensfroni the object and Von the focal length of the lens.V

The parts ofthe lens L at a greaterdistance from the object b result in an increased magnification andY in a removal of'pa'rts of ,the virtiniliniage farther from the transparency. By suitably choosing the Vstrength of the lens (focal length) 'and the' tip or inclination of the lens to the transparency,

any reasonable magnitude may beginn-to. beam'thanra tippedpla-nofcomfexylindrical the progressivefmagnilication of4 the t si red degree. l

Lampes" u 8 The relation of the object and virtual iinage are illustrated'l in Fig. 5whereintlie distance of the lens L from the object b, also the inclination of the lens L, and also the distance between object and virtual image,

,are yexafggeratedv for the purpose of clearness l.Assume a. beam of light passing through "point 1 of the object b, of which one ray e passes through lens L and is retracted along the line e', While another ray f is rcfracted along theliiie f; The virtual image of the point 1 will therefore appear at point 1 which is the iritersectionof the projection passing through a point of the object Z inimediatelybeloi'v the point 1 (indicated at 2 in Fig) will pass through the lower part .of the lens L and along lines in 4the -sanie vertical planes with e and f and be retracted along lines e2 and 2.- Tlie virtual image of the point 2, there ore, will be attlie intersection of projections of the lines e2 and f2 shownl at 2. The other corners 3 .and 4 of the object 'b ina similar manner produce virtual images 3' and 4', l

The virtual image b" is thus distorted and when projected Yupon the screen by a, beam oblique to the screen appears as an undistorted image e3 (Fig. 1) because the diston tion of the virtual i age b is equal and opposite to the distort-ion of the screen image 'due to the Obliquity ofthe beam and there- -fore n eutralizes it.

From the foregoing description it will be clear that not only may the keystone shape' of the projected image e corrected, but also the i'ertcal lengthening of the image on the screen which commonly results froin the fdownward inclination or obliquity of the beam to the screen. The positive cylindrical" l`lens niagnifies the image in the direction of the two lines e and f. Similarly, beams to the Obliquity of the beam such lateral niagnilication 'may be used to offset the vertical elongation of the image due to the Obliquity of the lieain to the screen. Thus, the apparatus neutralizes both types of dis,- toi'tion due to the Obliquity of the beam to the screen, namely, the keystone distortionand the elongation of the -ii'nage more in the direc-tion of one axis than the other.

The above described method and means for accomplishing the count-emotion of the screen distort-ion -is merely one exemplication of inyrim'ention; an it will be understood that other means maybe used fr prol diicin'g thereq-uired distortion of the image ies image .region is laterally magnified formly. l

10. Projection apparatus for producing on a screen which isoblique to the trans parency, a .magnified innige of the troni-i-4 -Earency, which is substantially free from eystone distortion, comprisingnieans for projecting u beam of light from the object to the screen, and refractng n ieiins tipped relatively to the transparency for laterally iefmcting the beam in varying degree from top to bottom, thereby producing in a plane normal thereto an image of varying lateral magnification of Such extent that the lateral magnification on the oblique screen isuniV--A4 11. Projection apparatus for producing on a screen which is oblique to the tianspareiicy, a iiiag'iiified i-niage of the transiarency, which is substantially free from cystone distortion, comprising refracting means tipped relatively to the transpai-'ency4 for producing a virtual image of thetriinspareiicy laterally distortedin a manner and to :in extent proportional and opposite to the lateral distortion of. the projected image due to the Obliquity of the screen.

12. Projection apparatus for produciifigir on a screen which is oblique vto the central ray of the beam of light striking the screen, a magnified, substantially iindistorted image of a transparency, coniprisiri" a,ylintl.i:f;cal.n lens for refracting thffrio ight passing *Frbiitlieolijectlo the screen, the cylindrical;

lens being inclined with relation to the optical axis, whereby there is produced in a plane normal to the beam an image of va ing .angular magnification such that the a solute magnification' on the oblique screen is uniform. Y

13. Projection apparatus for producing a. magnified image of a transparency on a screen which is oblique to 'the central ray of the beainfof light striking thefs'creen', comprising :i cylindrical lens tipped Vrelatively to the trans ar'encyfor refracting the' rays of vlight passing from the object to the screen, wherebyv there is produced in a plane normal to the beam an image of -vaiyi-iifr lat-eral magnification such thatthe laterarl magnification form- 14. Projection apparatus comprisin means for holding the object to be 'project-e "and a lens in 'the path of the projected 4image onthe oblique screen `is unihaving ditl'erent powers .in horizontal-:ind vertical plai'ies, jre s ectively, -ancl being tipped relatively tfo t e 'plane .of the object. i,

1o.-I )rojecti on a para-tus having` im opitical axis and :in -o ,]ecta positive cylindrical lens, :in objective 1en.s, 'an d' a screen, the

cylindrical lens afndthe screen being oblique to .the optical axis.

16. Projection 1 apparatus 1wherein the screen and the object are obli-(pic to each other, coinpi-ising'an objective ens end a rcfructing element obli-que to theoptlieal axis for neutralizing keystone distortion.

17. Projection appara-tos 'eoinprising an" 'a cylindrical lens 1nv objective lens a-.nc front of the objective ler'is and tipped relative-ly to the transparency.

18. Projection Aapparatus for producing,

on a screen which is oblique to the object,

-a magnified innige of the object which is beam in the region of the screen is laterally magnified nnifor'n-ily.

19. Projection apparat-us foivproduciig on a screen which is oblique tothe object, a magnified innige-of the object which isisubsis' stantially free from keystone distortion,

eonipiisiiig'ineans for projecting' abcaiii off lig-lit fronithe object to the screen, and light deflect/ingr means for laterally `deflectfin-zgj the beam in varying degree from top to bottom,

surface obl-ique to theoptical axis,

-the light deticct'ing means havingr an optical.

20. Projection apparatus-for producing,

on a screen 4ir-hielt is Oblique to :the object,

a magnified iinage of the object which' sub-- -stantiallyfree from Keystone distmrtiolfi,` c y eoniprisingiinea'ns for progecting .a beam of light from the object to. the screen, and light refracting means for laterally refra'eting the beam in varying degree `from top to bottor'n,

the light refracting means having an optica surface oblique to the. optical axis.

signed by 'ne ai. Boston, Massachusetts,

this Vletth day ofv June, 1915.

DANEL F., COZVSTCK.'

Witnesses: v c lReinier CUSHMAN, i

' RICHARD W. HALL.

4 .Mik 

